This invention relates to enclosures in a disk drive providing a reduced air gap around disk drive media surfaces within the enclosure.
Disk drives are an important data storage technology, which include several crucial components. Disk drive read-write heads directly communicate with a disk surface containing the data storage medium over a track on the disk surface. This invention involves improving the ability to position at least one read-write head over the track on the disk surface.
FIG. 1A illustrates a typical prior art high capacity disk drive 10 including actuator arm 30 with voice coil 32, actuator axis 40, suspension or head arms 50-58 with slider/head unit 60 placed among the disks 12.
FIG. 1B illustrates a typical prior art high capacity disk drive 10 with actuator 20 including actuator arm 30 with voice coil 32, actuator axis 40, head arms 50-56 and slider/head units 60-66 with all but one disk 12 removed as well as including spindle motor 80.
Since the 1980""s, high capacity disk drives 10 have used voice coil actuators 20-66 to position their read-write heads over specific tracks. The heads are mounted on head sliders 60-66, which float a small distance off the disk drive surface when in operation. Often there is one head per head slider for a given disk drive surface. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator.
Voice coil actuators are further composed of a fixed magnet actuator 20 interacting with a time varying electromagnetic field induced by voice coil 32 to provide a lever action via actuator axis 40. The lever action acts to move head arms 50-56 positioning head slider units 60-66 over specific tracks with speed and accuracy. Actuator arms 30 are often considered to include voice coil 32, actuator axis 40, head arms 50-56 and head sliders 60-66. Note that actuator arms 30 may have as few as a single head arm 50. Note also that a single head arm 52 may connect with two head sliders 62 and 64.
Today, read-write head positioning errors are a significant point of failure and performance degradation. These positioning errors are caused in part by disk fluttering. Some fluttering problems for disks can be attributed to instabilities in the motor turning the disk, which are being addressed by the motor manufacturers.
The disk drive industry faces some significant challenges. As either recording densities or spindle speed increases, both head positioning accuracy and head-flying stability must increase. Note that competitiveness in the disk drive industry requires both requires both increased recording density and increased spindle speeds. Note that head-flying is the motion of the read-write head over the disk surface, which flies a short distance off that surface.
In order to achieve an even higher track density essential for meeting the higher recording density requirements, the allowable position error of the heads relative to registered data tracks is required to be less than 0.05 xcexcm for the next few years.
New ways to improve head positioning and stabilize head-flying are needed to meet these challenges, as well as improve the reliability of existing disk drives.
The inventors have found that the above needs can be achieved through further reduction of disk fluttering and flow-induced vibration around actuator arms. High-speed rotation results in large amplitude vibration of the head-slider suspension and the arms. Thus the reduction of flow-induced vibration is essential to current and future disk drive to protect head-positioning failures.
Aerodynamics has been an area of active and continuing research since at least the nineteenth century. Prandtl defined boundary layers early in the twentieth century. The boundary layer concept was directly applicable to fluid flows involving air, water and other low viscosity fluids. The boundary layer is a fluid region near a surface with essentially no relative velocity with regards to that surface. This region is caused by the effect of friction between the solid surface and the fluid. The depth of this region is roughly proportional to the square root of the viscosity divided by the angular velocity of the surface.
The inventors have discovered that aerodynamic forces contribute to disk fluttering. If the air flow around these disk surfaces is unstable, the resulting aerodynamic forces can mechanically excite the disk surfaces, causing fluttering.
These aerodynamic forces act upon disk surfaces with respect to the air cavity in which the disk surfaces rotate. A rotating disk surface will tend to create a rotating boundary layer of air. This boundary layer will tend to rotate in parallel to the motion of the disk surface. The stationary surface of the disk drive cavity facing the disk surface will also tend to generate a boundary layer. The inventors discovered that when there is enough distance between the stationary surface and the disk surface for more than the boundary layer of the rotating disk surface, there is a back flow created against the direction of flow from the rotating disk surface.
The inventors have discovered that a significant reduction in disk surface mechanical fluttering results from reducing the air gap between stationary surfaces facing the disk surface to about the boundary layer thickness. The inventors have found that when the air gaps are approximately the boundary layer thickness, there is improved head positioning. When the air gaps are smaller fractions of the boundary layer thickness, there are further improvements in head positioning. These improvements are summarized for an operational rotating velocity of 5400 Revolutions Per Minute (RPM) in FIG. 3. Similar improvements are expected for other operating rotational velocities such as 7200 RPM, 10,000 RPM and over 14,000 RPM.
The invention includes not only the mechanical enclosures housing disk surfaces within a disk drive, but also the manufacturing methods, and the resulting disk drives. The disk drives may further be at most 13 millimeters in height.
These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.